The group tracked prices of the 35 most popular tech, home and personal care products on sale for the 2016 Black Friday weekend over the course of a year. Of those, 22 were from Currys/PC World, 12 from Argos and one from Amazon.

A Neff Slide and Hide Oven on offer for £494.99 at Currys/PC World last Black Friday was sold for £45 less just three weeks later, and was cheaper than the Black Friday price for at least 113 other days of the year.

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A Samsung 55-inch Smart 4K Ultra HD curved TV advertised by Currys as “Save £400, now £849” was £50 cheaper at least 29 times in December, January and April and £79 cheaper at least 18 times in May.

Currys also offered a DeLonghi bean-to-cup coffee machine for £349 for Black Friday in 2016, which it said was down from the £729.99 price for most of September and October. However, Which? found the coffee machine was sold for £579.99 for nearly three weeks during this time (Currys told the group this was an isolated mistake) and remained at the Black Friday price for almost all of December.

The Oral-B Pro 3000 crossaction electric toothbrush from Amazon was advertised as “save 26%: was £40.49, now £29.99” but was £5 cheaper on at least two days in July.

A 49-inch LG TV advertised by Argos at £499 as “Our lowest price” was £4 cheaper a week later and £16 cheaper at the end of December.

Alex Neill, Which? managing director of home products and services, said: “Our research shows that although Black Friday can offer some great discounts, not all offers are as good as they seem.

“It’s easy to get swept along by hype and excitement on the day, so we recommend doing some preparation and research to help make sure you really are getting a good deal when shopping in the sales.”

Currys/PC World told Which? it had reduced about 4,000 products for Black Friday 2016, adding: “We make no apology for reducing some of them even more after that period.”

Argos said: “Black Friday is a fantastic event which allows customers to choose from thousands of products which offer great value. This does not exclude these products from other sales or promotional activity at other times of the year.”

Amazon said: “We offer many thousands of incredible deals around Black Friday representing millions of pounds of savings for our customers across a vast selection of products.”

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